In a power semiconductor device controlling electric power, an element having a symmetrical structure in a semiconductor substrate surface is generally formed in view of equalizing breakdown electric field strength or the like. In other words, the element is so laid out that the shape of the element is symmetrical (line-symmetrical or point-symmetrical) when the semiconductor substrate is viewed directly from above. The element is formed on a prescribed crystal growth layer grown on the surface of the semiconductor substrate. When the angle (offset angle) formed by the substrate surface and a crystal plane in the crystal growth is 0 degrees in the semiconductor substrate, the angle formed by the surface of the crystal growth layer epitaxially grown on the surface of the semiconductor substrate and the crystal plane of the crystal growth layer is 0 degrees. Therefore, it follows that the symmetry of the shape of the element formed on the crystal growth layer is reflected and an element structure also three-dimensionally symmetrical is obtained.
In a semiconductor device employing SiC (silicon carbide) as the semiconductor device, however, it does not follow that a symmetrical element structure is obtained in three-dimensional structure in consideration of substrate crystal orientation even if the element shape is laid out to be line-symmetrical when the semiconductor substrate is viewed directly from above, since the crystal plane of SiC has no plane symmetry and an inclined substrate whose surface forms an angle of several degrees with the crystal plane is employed due to limitation on the conditions for epitaxial growth of SiC.
Considering surfaces (sidewalls or side surfaces of the periphery) extending in the depth direction of an implantation region constituting a diode or the like, for example, the directions of electric fields formed in voltage application on parallel surfaces of the periphery opposite to each other in the direction of inclination corresponds to the directions of crystal plane orientations whose crystal orientations are different from each other by 180 degrees. Considering the sidewalls of the periphery located on the downstream side and the upstream side of the direction of inclination respectively, it follows that the angles formed with the crystal plane vary with the sidewall located on the downstream side and the sidewall located on the upstream side. Patent Document 1 is cited as a document disclosing such a semiconductor device employing SiC.
Patent Document 1: Japanese Patent Laying-Open No. 2000-188406